Suspension sub frame structure

ABSTRACT

A suspension sub frame structure comprises a suspension sub frame provided to extend in a vehicle longitudinal direction and supporting a suspension link, an extension frame provided to extend forwardly from a front end of the suspension sub frame and having lower rigidity against a load applied in the vehicle longitudinal direction than the suspension sub frame, and a cross member provided to extend in a vehicle width direction on an inward side, in the vehicle width direction, of the both frames, wherein the cross member is joined to the both frames at a joint area which is continuous in the vehicle longitudinal direction.

BACKGROUND OF THE INVENTION

The present invention relates to a suspension sub frame structure.

A vehicle-body front structure, in which a pair of right-and-left frontside frames extending in a vehicle longitudinal direction andconstituting a vehicle-body front portion are provided and a suspensionsub frame (hereafter, referred to as “sub frame” simply) provided belowthe front side frames and supporting right-and-left suspension links ofa front wheel is provided, is known.

The sub frame of a vehicle-body front structure disclosed in JapanesePatent Laid-Open Publication No. 2015-58856 (US Patent ApplicationPublication No. 2015/0083514 A1) comprises right-and-left side partswhich are arranged below the front side frames and a front side partwhich interconnects respective front ends of the right-and-left sideparts in a vehicle width direction, wherein the sub frame is configuredin a U shape which is opened to a vehicle rearward side in a plan view.This sub frame is fixed to the front side frames at respective rear endportions of the right-and-left side parts. A tower member which isconfigured to rise from a front end portion of each of theright-and-left side parts and connected to a lower face of each of thefront side frames is attached to each of the front side frames. Anextension frame which extends forwardly from a middle position, in avertical direction, of the tower member is attached to the tower member.

In the structure of the above-described patent document, an impact loadinputted from a vehicle forward side is dispersed and transmitted to thefront side frame through a main load path where the impact load isinputted directly to the front side frame and another load path wherethe impact load is inputted from the extension frame to the front sideframe by way of the tower member. Thus, the impact load can be dispersedby providing the other load path where the impact load is inputted byway of the extension frame.

The above-described extension frame serves as an impact absorbing memberto absorb the impact load by being deformed when receiving the impactload from the vehicle forward side. The tower member serves as a loadreceiving portion to receive the impact load inputted by way of theextension frame so as to make the extension frame absorb the impact loadsecurely.

In the vehicle-body front structure of the above-described patentdocument, the extension frame is connected to a middle part of the towermember. Therefore, it is necessary that the tower member is formedrigidly in order that the extension frame attains its impact-loadabsorption sufficiently by suppressing bending deformation of the towermember when the impact load is inputted from the vehicle forward side.However, this rigidly-forming of the tower member may cause an improperincrease of the vehicle weight, so that there is room for improvement indecreasing the vehicle weight.

Herein, it may be considered to create a load path which extends fromthe extension frame by way of the side part of the sub frame and thenreaches the front side frame from the rear end portion of the side partof the sub frame. In this case, it may be considered that a rear endportion of the extension frame is directly connected to the front endportion of the side part of the sub frame which has high rigidity in thelongitudinal direction. Thereby, the sub frame can serve as the loadreceiving portion to receive the impact load inputted to the extensionframe from the vehicle forward side, thereby promoting the impactabsorption performance of the extension frame.

However, in a case where the extension frame is directly connected tothe sub frame as described above, it is likely that bending or breakageoccur at a connection portion of the extension frame which placesimportance on the impact-load absorption performance and the sub framewhich places importance on the rigidity in the longitudinal directionwhen a load in a bending direction is inputted by buckling of theextension frame.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide asuspension sub frame structure which can compatibly attain effectivelyperforming the respective functions of the extension frame and thesuspension sub frame and suppressing the bending or breakage of theconnection portion of these frames, suppressing the increase of thevehicle weight.

The present invention is a suspension sub frame structure, comprising asuspension sub frame provided to extend in a vehicle longitudinaldirection and supporting a suspension member of a front wheel, anextension frame provided to extend forwardly from a front end of thesuspension sub frame and having lower rigidity against a load applied inthe vehicle longitudinal direction than the suspension sub frame, and across member provided to extend in a vehicle width direction on aninward side, in the vehicle width direction, of the suspension sub frameand the extension frame, wherein the cross member is joined to thesuspension sub frame and the extension frame at a joint area which iscontinuous in the vehicle longitudinal direction.

According to the present invention, since the extension frame having thelower rigidity than the suspension sub frame is connected to the frontend of the suspension sub frame, the impact load inputted from thevehicle forward side is received by the suspension sub frame, so thatthe effective impact absorption can be attained by deformation of theextension frame.

Further, since the cross member extending in the vehicle width directionis joined to the suspension sub frame and the extension frame at thejoint area which is continuous in the vehicle longitudinal direction, aconnection portion of the both frames is reinforced by the cross member.Accordingly, even in a case where the load in the bending direction isinputted to the connection portion of the suspension sub frame and theextension frame by buckling deformation of the extension frame when theimpact load is inputted from the vehicle forward side, improper bendingor breakage of the connection portion can be suppressed.

In an embodiment of the present invention, the cross member comprises anupper-face joint portion which is joined to an upper face of theextension frame and an upper face of the suspension sub frame at thejoint area and a lower-face joint portion which is joined to a lowerface of the extension frame and a lower face of the suspension sub frameat the joint area.

According to this embodiment, the cross member is joined to therespective upper faces and the respective lower faces of the extensionframe and the suspension sub frame at its upper-face joint portion andits lower-face joint portion in the joint area of the cross member suchthat the cross member is continuous to the both frames. That is, thecross member is joined in such a manner that it holds the upper facesand the lower faces of the both frames from a vehicle inward side.Thereby, the rigidity, in the vertical direction, of the connectionportion, of the both frames, in particular, can be more increased, sothat the bending or breakage of the connection portion can beeffectively suppressed.

In another embodiment of the present invention, the joint area comprisesa front-side joint area where the cross member is joined to theextension frame and a rear-side joint area where the cross member isjoined to the suspension sub frame, and the front-side joint area isshorter than the rear-side joint area.

According to this embodiment, since the longitudinal dimension of thejoint area is set such that the front-side joint area where the crossmember is joined to the extension frame is relatively short compared tothe rear-side joint area where the cross member is joined to thesuspension sub frame, it is suppressed that the impact absorptionperformed by the extension frame is improperly blocked by the crossmember at the front-side joint area when the impact load is inputtedfrom the vehicle forward side.

Meanwhile, since the longitudinal dimension of the joint area is setsuch that the rear-side joint area where the cross member is joined tothe suspension sub frame is relatively long compared to the front-sidejoint area where the cross member is joined to the extension frame, therigidity of the suspension sub frame against the load in the vehiclelongitudinal direction is more increased at the rear-side joint area.Thereby, when the impact load is inputted from the vehicle forward side,the impact absorption performance of the extension frame can beeffectively promoted.

In another embodiment of the present invention, a bracket to make thesuspension sub frame support the suspension member is attached to theextension frame and the suspension sub frame at an area which iscontinuous in the vehicle longitudinal direction.

According to this embodiment, since the bracket to make the suspensionsub frame support the suspension member is attached to the extensionframe and the suspension sub frame at the area which is continuous inthe vehicle longitudinal direction, the connection portion of the bothframes is reinforced more rigidly. Thereby, even in the case where theload in the bending direction is inputted to the connection portion ofthe suspension sub frame and the extension frame when the impact load isinputted from the vehicle forward side, the bending or breakage of theconnection portion is suppressed more effectively.

Other features, aspects, and advantages of the present invention willbecome apparent from the following description which refers to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle-body front portion which isprovided with a suspension sub frame structure according to anembodiment of the present invention.

FIG. 2 is a side view of the vehicle-body front portion which isprovided with the suspension sub frame structure according to theembodiment of the present invention.

FIG. 3 is a plan view of the suspension sub frame structure according tothe embodiment of the present invention.

FIG. 4 is an enlarged view of a joint portion of a suspension sub frame,an extension frame, and a second cross member which are shown in FIG. 3.

FIGS. 5A, 5B, 5C and 5D are respective sectional views taken along linesA-A, B-B, C-C and D-D of FIG. 4.

FIG. 6 is an enlarged bottom view of a major part of the joint portionof the suspension sub frame, the extension frame, the second crossmember, and a front-side bracket.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, a suspension sub frame structure according to an embodimentof the present invention will be specifically described.

A front vehicle-body structure 1 which is provided with a suspension subframe structure of the present embodiment will be specifically describedreferring to FIGS. 1-3.

As shown in FIGS. 1 and 2, the front vehicle-body structure 1 comprisesa pair of right-and-left front side frames 20, 20 which extend in thevehicle longitudinal direction, a dash cross 30 which is arranged alonga front face of a dash panel (not illustrated) and interconnects theboth front side frames 20, 20, and a suspension sub frame structure 100which is arranged below the both front side frames 20, 20.

A vehicle of the present embodiment adopts a front-engine rear-drive(FR) type. A powertrain 4 which comprises a longitudinal arrangementtype of engine 41 and a transmission 42 which is connected to a rearpart of the engine 41 is provided in an engine room E between the frontside frames 20, 20 (see FIG. 3).

Each of the front side frames 20, 20 comprises a front-side linear part21 which extends forwardly from the dash cross 30 nearly horizontally, aslant part 22 which extends obliquely rearwardly-and-downwardly from arear end portion of the front-side linear part 21, and a rear-sidelinear part 23 which extends rearwardly from a lower end portion of theslant part 22 nearly horizontally.

The front-side linear part 21 of the front side frame 20 comprises aninner panel 24 which is positioned on an inward side in the vehiclewidth direction and an outer panel 25 which is positioned on an outwardside in the vehicle width direction, which are joined together in thevehicle width direction. The inner panel 24 is configured to have ahat-shaped cross section which is opened to the vehicle outward side,and the outer panel 25 is configured to have a hat-shaped cross sectionwhich is opened to the vehicle inward side. These panels 24, 25 extendin the vehicle longitudinal direction, respectively. The outer panel 25and the inner panel 24 are joined together at the respectiveupper-and-lower edge portions. Thereby, the front-side linear part 21 isconfigured to have a closed cross section which is continuous in thevehicle longitudinal direction.

The slant part 22 of the front side frame 20 is configured to have ahat-shaped cross section which is opened to the vehicle upward side. Theslant part 22 is arranged along a shape of the dash panel (notillustrated) such that its rearward side is located at a lower level,and an upper edge portion of the slant part 22 is joined to the dashpanel. Thereby, a closed cross section which is continuous in thevehicle longitudinal direction is formed between the slant part 22 andthe dash panel.

The rear-side linear part 23 of the front side frame 20 is connected toa front end portion of the floor frame (not illustrated) extending inthe vehicle longitudinal direction at its rear end portion. A floorpanel (not illustrated) is joined onto the rear-side linear part 23 andthe floor frame, and a front end edge of the floor panel is connected tothe dash panel. The rear-side linear part 23 and the floor frame arerespectively configured to have a hat-shaped cross section which isopened to the vehicle upward side, and a closed cross section extendingin the vehicle longitudinal direction is formed between the floor paneland each of the rear-side linear part 23 and the floor frame.

A main crash can 53 is connected to a front end of each of the frontside frames 20, 20 via a set plate 51 and an attaching plate 52, whereinthe main crash can 53 is made of a cylindrical member or the like whichabsorbs the impact load inputted from the vehicle forward side. A bumperreinforcement 54 which extends in the vehicle width direction isattached to respective front end faces of the right-and-left crash cans53.

Next, referring to FIG. 3 in addition to FIGS. 1 and 2, the suspensionsub frame structure 100 will be described. The suspension sub framestructure 100 comprises a pair of right-and-left suspension sub frames110, 110 which are arranged below the front side frames 20, 20 andsupport lower arms 60, 60 as suspension links for a pair of frontwheels, a pair of right-and-left extension frames 130, 130 which arejoined to front ends of the suspension sub frames 110, 110 and extendforwardly, and first-third cross members 140, 150, 160 whichrespectively interconnect the right-and-left frames 110, 110, 130, 130.

A sub crash can 55 is configured to extent forwardly from a front endportion of each of the extension frames 130, 130. A sub bumperreinforcement 58 which extends in the vehicle width direction isprovided in front of the right-and-left sub crash cans 55, 55. Theright-and-left sub crash cans 55, 55 are interconnected via the subbumper reinforcement 58.

Each of the lower arms 60, 60 supported at the suspension sub frames110, 110 comprises a front-side arm portion 61 which extends in thevehicle width direction nearly horizontally and a rear-side arm portion62 which extends inwardly-and-rearwardly from a middle portion, in thevehicle width direction, of the front-side arm portion 61 linearlyhorizontally. The lower arm 60 is configured to have a linearly L shapeas a whole in a plan view.

The lower arm 60 is provided with a front-side connection portion 61 aand a rear-side connection portion 62 a which are positioned on theinward side, in the vehicle width direction, of the lower arm 60. Thefront-side connection portion 61 a is connected to a relatively forwardsection of the suspension sub frame 110, and the rear-side connectionportion 62 a is connected to a relatively rearward section of thesuspension sub frame 110. The front-side connection portion 61 a isformed at an inward end portion, in the vehicle width direction, of thefront-side arm portion 61, and the rear-side connection portion 62 a isformed at a rear end portion of the rear-side arm portion 62.

The front-side connection portion 61 a of the front-side arm portion 61is pivotally supported at a front-side bracket 63 which is attachedbetween a front end portion of the suspension sub frame 110 and a rearend portion of the extension frame 130 such that the front-side armportion 61 rotates around an axis extending in the vehicle longitudinaldirection. Meanwhile, the rear-side connection portion 62 a of therear-side arm portion 62 is pivotally supported at a rear-side bracket64 which is attached to the suspension sub frame 110 such that therear-side arm portion 62 rotates around an axis extending in the vehiclelongitudinal direction.

As shown in FIGS. 4 and 5, the suspension sub frame 110 includes a bodypart 111 which supports the lower arm 60. The rear end portion of theextension frame 130 is connected to a front end portion 112 of the bodypart 111 of the suspension sub frame 110. Herein, a rear end portion 113of the body part 111 is fixed to the front side frame 20 via a rear-sidevehicle-body attachment portion X3 which will be described later.

The body part 111 of the suspension sub frame 110 is an elongatedportion which is configured to extend in the vehicle longitudinaldirection. The body part 111 comprises an upper member 114 which isconfigured to have a U-shaped cross section which is opened to thevehicle downward side and a lower member 115 which is configured to havea U-shaped cross section which is opened to the vehicle upward side. Alower edge portion of the upper member 114 and an upper edge portion ofthe lower member 115 are joined together by welding, for example. Thebody part 111 is configured to have a closed cross section which isformed between the upper member 114 and the lower member 115.

Specifically, the upper member 114 comprises an upper face portion 114a, an outward-side face portion 114 b, and an inward-side face portion114 c, and the lower member 115 comprises a lower face portion 115 a, anoutward-side face portion 115 b, and an inward-side face portion 115 c.The outward-side face portions 114 b, 115 b and the inward-side faceportions 114 c, 115 c of the upper member 114 and the lower member 115are joined, respectively, thereby forming the closed cross sectionextending in the vehicle longitudinal direction (see FIG. 5D).

An opening portion 116 (see FIG. 5A) is formed by the upper member 114and the lower member 115 at the front end portion 112 of the body part111 of the suspension sub frame 110.

As shown in FIGS. 5A and 5C, the extension frame 130 is, similarly tothe body part 111 of the suspension sub frame 110, configured to have aclosed cross section extending in the vehicle longitudinal direction,which is formed by an upper member 131 which is configured to have aU-shaped cross section which is opened to the vehicle downward side anda lower member 132 which is configured to have a U-shaped cross sectionwhich is opened to the vehicle upward side.

Specifically, the upper member 131 comprises an upper face portion 131a, an outward-side face portion 131 b, and an inward-side face portion131 c, and the lower member 132 comprises a lower face portion 132 a, anoutward-side face portion 132 b, and an inward-side face portion 132 c.The outward-side face portions 131 b, 132 b and the inward-side faceportions 131 c, 132 c of the upper member 131 and the lower member 132are joined, respectively, thereby forming the closed cross sectionextending in the vehicle longitudinal direction (see FIG. 5C).

Herein, the rear end portion 133 of the extension frame 130 isconfigured to have a smaller outer diameter than a part of the extensionframe 130 which is positioned on the forward side of the rear endportion 133.

The both frames 110, 130 are connected to each other by inserting therear end portion 133 of the extension frame 130 into the opening portion116 of the front end portion 112 of the body part 111 of the suspensionsub frame 110 (see FIG. 5A). The both frames 110, 130 are joined bywelding or the like, for example, at a connection portion 80 of theseframes 110, 130. Thereby, the extension frame 130 and the suspension subframe 110 are integrally continuous in the vehicle longitudinaldirection (see FIG. 5A).

In the present embodiment, the rigidity of the extension frame 130against the inputted load in the vehicle longitudinal direction is setto be lower than that of the suspension sub frame 110. Thereby, theextension frame 130 and the suspension sub frame 110 which arecontinuous in the vehicle longitudinal direction can perform differentfunctions. Specifically, the suspension sub frame 110 which ispositioned on the rearward side and has the relatively high rigidity canserve as a load receiving portion, whereas the extension frame 130 whichis positioned on the forward side and has the relatively low rigiditycan perform the load absorption function.

Next, the first-third cross members 140, 150, 160 which are providedbetween the right-and-left suspension sub frames 110, 110 and theright-and-left extension frames 130, 130 of the suspension sub framestructure 100 will be described referring to FIG. 3.

The frame-shaped roughly-linear first cross member 140 is attached tothe front end portions 134, 134 of the pair of right-and-left extensionframes 130, 130 so as to interconnect (bridge) the front end portions134, 134 in the vehicle width direction.

The connection portion 80 of the right-side suspension sub frame 110 andthe right-side extension frame 130 and another connection portion of theleft-side suspension sub frame 110 and the left-side extension frame 130are interconnected via the second cross member 150.

The second cross member 150 comprises a front side portion 151 whichextends in the vehicle width direction between the right-and-leftextension frames 130, 130 and interconnects these extension frames 130,130, right-and-left side portions 152, 152 which extend rearwardly fromright-and-left both end portions of the front side portion 151, and areinforcing frame 153 which is arranged between the right-and-left sideportions 152, 152. The reinforcing frame 153 comprises a lateral frameportion 154 which extends in the vehicle width direction between theright-and-left side portions 152, 152 and interconnects respective rearend portions of these side portions 152, 152 and a longitudinal frameportion 155 which extends in the vehicle longitudinal direction betweenthe lateral frame portion 154 and the front side portion 151 andinterconnects these portions 154, 151.

As shown in FIG. 5B, the front side portion 151 comprises an uppermember 156 which is configured to extend in the vehicle width directionand have a U-shaped cross section which is opened to the vehicledownward side and a plate-shaped lower member 159 which is configured toclose an opening face of the upper member 156. The lower member 159 isconfigured to have a wider width, in the vehicle longitudinal direction,than the upper member 156 and protrude rearward beyond the upper member156. Further, the lower member 159 is arranged over an area, in thevehicle longitudinal direction, between the extension frame 130 and thesuspension sub frame 110.

The upper member 156 of the front side portion 151 comprises an upperface portion 156 a, a front face portion 156 b, and a rear face portion156 c. The upper member 156 is provided at an upper face 159 a of thelower member 159, and the front face portion 156 b is provided along afront end portion 159 b of the lower member 159. Respective lower endportions of the front face portion 156 b and the rear face portion 156 care joined to the upper face 159 a of the lower member 159, so that aclosed cross section extending in the vehicle width direction is formedbetween the upper member 156 and the lower member 159.

As shown in FIG. 5C, the upper face portion 156 a of the front-sideupper member 156 is joined to the respective upper face portions 131 a,131 a of the extension frames 130, 130 at both edge portions 156 d, 156d, in the vehicle width direction, of the upper face portion 156 a.

As shown in FIGS. 5C and 5D, both end portions 159 c, 159 c, in thevehicle width direction, of the lower member 159 are joined to the lowerface portions 132 a, 132 a of the extension frames 130, 130 and thelower face portions 115 a, 115 a of the body parts 111, 111 of thesuspension sub frames 110, 110.

As shown in FIG. 5D, the right-and-left side portions 152, 152 compriseupper members 157, 157 which are integrally continuous to theabove-described front-side-portion upper member 156 and theabove-described lower member 159. This upper member 157 is provided toextend in the vehicle longitudinal direction and be continuous to thefront-side-portion upper member 156 at its front end portion. Thereby,the front-side-portion upper member 156 and the upper members 157, 157of the right-and-left side portions 152, 152 are configured to have aU-shaped cross section which is opened to the vehicle rearward side as awhole in the plan view (see FIG. 3).

The upper member 157 of the side portion 152 is configured such that itsinner edge portion 157 b is located at a lower level than its outer edgeportion 157 a. Further, this upper member 157 comprises a slant portion157 c which is configured to gradually lower as it goes from the outeredge portion 157 a to the inner edge portion 157 b.

The inner edge portions 157 b, 157 b of the above-described uppermembers 157, 157 are joined to the upper face 159 a of the lower member159, and the outer edge portions 157 a, 157 a are joined to the upperface portions 114 a, 114 a of the body parts 111, 111 of the suspensionsub frames 110, 110.

Thereby, a closed cross section extending in the vehicle longitudinaldirection is formed by the upper member 157, the lower member 159, andthe inward-side face portions 114 c, 115 c of the body part 111 of thesuspension sub frame 110.

As shown in FIG. 3, each of the right-and-left side portions 152, 152 ofthe second cross member 150 is configured such its width is graduallyenlarged toward the vehicle forward side in the plan view. Thereby, areinforcing portion 151A having an arc-shaped contour is formed at eachcorner portion between the front side portion 151 and the right-and-leftside portions 152, 152. Thereby, the rigidity of the lower arm 60 of thesuspension device against a lateral force is increased, so that thesuspension sub frame 110 and the extension frame 130 are suppressed frombeing deformed inwardly in the vehicle width direction.

As described above, the second cross member 150 comprises the nearlyT-shaped reinforcing frame 153 which is formed by the lateral frameportion 154 interconnecting the respective rear end portions of theright-and-left side portions 152, 152 and the longitudinal frame portion155 interconnecting the middle portion of the lateral frame portion 154and the middle portion of the front side portion 151.

As shown in FIG. 5B, the lateral frame portion 154 is configured to havea U-shaped cross section which extends in the vehicle width directionand is opened to the vehicle downward side. Meanwhile, the longitudinalframe portion 155 is configured to have a U-shaped cross section whichextends in the vehicle longitudinal direction and is opened to thevehicle downward side.

The lateral frame portion 154 comprises an upper face portion 154 a, afront face portion 154 b, and a rear face portion 154 c, wherein therear face portion 154 c is positioned along the rear end portion 159 dof the lower member 159. The front face portion 154 b and the rear faceportion 154 c of the lateral frame portion 154 are joined to the upperface 159 a of the lower member 159. Thereby, a closed cross sectionwhich is continuous in the vehicle width direction is formed between thelateral frame portion 154 and the lower member 159. Herein, both sideportions 154 d, 154 e of the lateral frame portion 154 are respectivelyjoined to the slant portions 157 c, 157 c of the right-and-left sideportions 152, 152 (see FIGS. 3 and 4).

The longitudinal frame portion 155 comprises an upper face portion 155 aand both side face portions 155 b, 155 b in the vehicle width direction,and respective lower end portions of the both side face portions 155 b,155 b are joined to the lower member 159. Thereby, a closed crosssection extending in the vehicle longitudinal direction is formedbetween the longitudinal frame portion 155 and the lower member 159.Herein, a front end portion 155 c of the longitudinal frame portion 155is joined to the rear face portion 156 c of the front side portion 151.

Herein, a joint area Z of the second cross member 150 and the suspensionsub frame 110 and the extension frame 130 will be described later.

As shown in FIG. 3, there is provided the third cross member 160 whichinterconnects the respective rear end portions 113, 113 of thesuspension sub frames 110, 110 in the vehicle width direction. The thirdcross member 160 is a plate member extending in the vehicle widthdirection which is fixed to the rear end portions 113, 113 of thesuspension sub frames 110, 110 from below with plural bolts 161 . . .161 or the like.

Further, as shown in FIG. 2, the above-described sub frame structure 100is provided with three sets of attachment portions to the frontsideframes 20, 20, i.e., front-side vehicle-body attachment portions X1, X1,middle vehicle-body attachment portions X2, X2, and the rear-sidevehicle-body attachment portions X3, X3, at its right-and-left bothsides. Hereafter, these will be specifically described.

The front-side vehicle-body attachment portion X1 is formed by aconnecting member 71 which is provided at the front end portion 134 ofthe extension frame 130. Specifically, the connecting member 71 isconfigured in a tower shape such that its lower part 72 is connected tothe extension frame 130 and the other part extends upwardly.

Further, the connecting member 71 is of a hollow boxy shape, and anupper face portion 73 of an outward-side portion, in the vehicle widthdirection, thereof is attached to a lower face 25 a of the outer panel25 of the front side frame 20 via a mount bush 74 by using a fasteningmember 75.

Herein, the sub crash can 55 is connected to a vertical-wall shapedfront face 76 of the connecting member 71 via an attaching plate 57.

The middle vehicle-body attachment portion X2 is formed by a powertrainmount bracket (hereafter, referred to as “mount bracket” simply) 90. Anengine mount (not illustrated) for resiliently supporting the powertrain4 (see FIG. 3) is stored at the mount bracket 90. The mount bracket 90is fixed to the body part 111 of the suspension sub frame 110. In thepresent embodiment, the mount bracket 90 is integrally made of diecast,such as aluminum diecast. However, a material of the mount bracket 90should not be limited to aluminum.

A hollow-shaped storage portion 91 with a storage space which is openedto the vehicle upward side is formed at the mount bracket 90. Thisstorage portion 91 is of a cylindrical shape, for example. A mountsupport structure which is connected to a powertrain-side bracketprovided at the powertrain 4 is stored in the storage portion 91.

The mount bracket 90 is provided with plural fastening portions 92, 93,94 for fastening to the suspension sub frame structure 100. The pluralfastening portions 92, 93, 94 comprise a front-side fastening portion 92which is provided at a front edge portion of the mount bracket 90, arear-side fastening portion 93 which is provided at a rear end portionof the mount bracket 90, and a middle fastening portion 94 which isprovided between the front-side fastening portion 92 and the rear-sidefastening portion 93.

Specifically, the fastening portions 92, 93, 94 are formed by pluralflange portions 92 a, 93 a, 94 a which are configured to extendoutwardly from a lower end portion of an outer peripheral portion 91 aof the storage portion 91 of the mount bracket 90. These flange portions92 a, 93 a, 94 a have bolt insertion holes (not illustrated), throughwhich bolts are inserted, whereby the flange portions 92 a, 93 a, 94 aare fastened to the suspension sub frame structure 100.

Meanwhile, the suspension sub frame 110 is provided with bolt fasteningholes 111 a, 111 b for attaching the mount bracket 90 which are locatedat positions which correspond to the above-described bolt insertionholes of the front-side fastening portion 92 and the rear-side fasteningportion 93 of the mount bracket 90, respectively (see FIG. 4).

Each of the right-and-left side portions 152, 152 of the second crossmember 150 is provided with a bolt fastening hole 152 a for attachingthe mount bracket 90 which is located at a position which corresponds tothe bolt insertion hole of the middle fastening portion 94. Herein, themiddle fastening portion 94 is fastened to the vicinity of a rear endportion of the side portion 152 nearly at the same position, in thevehicle longitudinal direction, as the lateral frame portion 154.Thereby, it is suppressed that the mount bracket 90 is displaced in sucha manner that it falls down inwardly (so-called inward falling down).

Bolts 92 c, 93 c, 94 c which are inserted into the bolt insertion holesof the mount bracket 90 and the bolt insertion holes 111 a, 111 b, 152 aof the suspension sub frame 110 and the side portion 152 are screwedinto weld nuts, not illustrated, which are provided at the lower faces115 a, 159 of the suspension sub frame 110 and the side portion 152.Thereby, the mount bracket 90 is fastened to the suspension sub frame110.

The mount bracket 90 is provided with a protrusion portion 95 whichextends outwardly-and-upwardly from an outer edge, in the vehicle widthdirection, of an upper wall face portion 91 b of the storage portion 91.A pole-shaped portion 95 b which protrudes upwardly is provided at anoutward end portion 95 a, in the vehicle width direction, of theprotrusion portion 95. The pole-shaped portion 95 b is attached to thelower face 25 a of the outer panel 25 with a bolt 95 c at a rear portionof the front-side liner part 21 of the front side frame 20, whereby themiddle vehicle-body attachment portion X2 is formed. Herein, the middlevehicle-body attachment portion X2 is rigidly joined to the front sideframe 20 via no damping element, such as a rubber bush.

The rear-side vehicle-body attachment portion X3 is, as shown in FIGS. 2and 3, provided beside the rear end portion 113 of the body part 111 ofthe suspension sub frame 110. The rear-side vehicle-body attachmentportion X3 comprises an upper-side plate member 121 and a lower-sideplate member 122.

The upper-side plate member 121 and the lower-side plate member 122respectively comprise, as shown in FIG. 4, side edge portions 121 a, 122a which extend in parallel to the outward-side faces 114 b, 115 b of thesuspension sub frame 110, front edge portions 121 b, 122 b which extendobliquely rearwardly-and-outwardly, and rear edge portions 121 c, 122 cwhich connect the side edge portions 121 a, 122 a and rear end portionsof the front edge portions 121 b, 122 b, which are of a nearlytriangular shape as a whole in the plan view.

The upper-side plate member 121 and the lower-side plate member 122 arejoined together by welding respective flange portions (not illustrated)provided at their rear edge portions 121 c, 122 c.

The side edge portion 121 a of the upper-side plate member 121 is joinedto the rear portion of the body part 111 of the suspension sub frame 110by welding, for example, and the side edge portion 122 a of thelower-side plate member 122 is joined to the lower face 115 a of therear portion of the body part 111 of the suspension sub frame 110.Thereby, the rear-side vehicle-body attachment portion X3 is joined tothe body part 111 of the suspension sub frame 110.

The upper-side plate member 121 and the lower-side plate member 122 ofthe rear-side vehicle-body attachment portion X3 are provided with boltinsertion holes 121 e, 122 e for fastening the suspension sub frame 110to the front side frame 20 at a position which is outwardly, in thevehicle width direction, spaced apart from the body part 111 of thesuspension sub frame 110.

A sleeve member 124 (see FIG. 1) to be fixed to the front side frame 20with a bolt 125 is interposed between the upper-side plate member 121and the lower-side plate member 122. This sleeve member 124 is connectedto the body part 111 via the upper-side plate member 121 and thelower-side plate member 122.

Meanwhile, a bracket 26 for fixing the rear-side vehicle-body attachmentportion X3 is joined to the rear end portion of the slant part 22 of thefront side frame 20 from below. A weld nut (not illustrated) into whichthe bolt 125 is screwed is attached to an upper face of the bracket 26.

At the rear-side vehicle-body attachment portion X3, a tip portion ofthe bolt 125 which is inserted from below into the bolt insertion hole122 e of the lower-side plate member 122, a hole (not illustrated) ofthe sleeve member 124, and the bolt insertion hole 121 e of theupper-side plate member 121 is screwed into the above-described weld nutof the bracket 26. Thereby, the suspension sub frame 110 is fixedlyfastened to the lower face of the front side frame 20 at the rear-sidevehicle-body attachment portion X3.

Next, a move (operation) of the suspension sub frame structure 100according to the present embodiment when the impact load is inputtedfrom a vehicle forward side will be described.

The impact load inputted to the bumper reinforcement 54 from the vehicleforward side is transmitted to the vehicle rearward side by way of themain crash cans 53, 53 and the front side frames 20, 20. The impact loadinputted to the sub bumper reinforcement 58 from the vehicle forwardside is transmitted to the front side frames 20, 20 by way of the subcrash cans 55, 55, the extension frames 130, 130, the body parts 111,111 of the suspension sub frame 110, 110, and the rear-side attachmentportions X3, X3. Thus, the impact load transmission route toward thevehicle rearward side can be dispersed into two load paths.

Further, when the relatively-large impact load is inputted to the bumperreinforcement 54 and the sub bumper reinforcement 58 from the vehicleforward side, the main crash cans 53, 53 and the sub crash cans 55, 55are crushed, thereby attaining the impact absorption. Part of the impactload which has not been absorbed through crushing of the crash cans 53,53, 55, 55 is inputted to the respective front end portions of the frontside frames 20, 20 and the extension frames 130, 130, and thentransmitted toward the vehicle rearward side through the above-describedtwo load paths.

When the larger impact load is inputted from the vehicle forward side,the impact load is absorbed by deformation of the front side frames 20,20 and the extension frames 130, 130. Herein, since the suspension subframes 110, 110 effectively serve as the load receiving portions becauseof the above-described structure with the closed cross section, theimpact absorption performance of the extension frames 130, 130 isproperly increased.

Hereafter, the joint area Z of the second cross member 150 and theextension frame 130 and the suspension sub frame 110 will be describedspecifically referring to FIG. 4 primarily.

As shown in FIG. 4, the outward-side end portion of the second crossmember 150 is joined to the extension frame 130 and the suspension subframe 110 over the longitudinally-continuous joint area Z.

More specifically, as described above, the outer edge portion 156 d ofthe front-side-portion upper member 156 and the outer edge portion 157 aof the side-portion upper member 157 of the second cross member 150 arerespectively joined to the upper face portion 131 a of the rear endportion 133 of the extension frame 130 and the upper face portion 114 aof the front end portion 112 of the suspension sub frame 110 as anupper-face joint portion Z1 (see FIGS. 5C and 5D).

Further, the both end portions 159 c, 159 c of the lower member 159 ofthe second cross member 150 are respectively joined to the lower faceportion 132 a of the rear end portion 133 of the extension frame 130 andthe lower face portion 115 a of the front end portion 112 of thesuspension sub frame 110 as a lower-face joint portion Z2 (see FIGS. 5Cand 5D).

Thereby, the second cross member 150 is joined to the both frames 110,130 in such a manner that it holds the connection portion 80 of theextension frame 130 and the suspension sub frame 110 from the vehicleinward side at the longitudinally-continuous joint area Z. Accordingly,it is suppressed that the connection portion 80 of the both frames 110,130 which have different functions is bent or broken in the verticaldirection or inwardly in the vehicle width direction, in particular,when the impact load is inputted from the vehicle forward side.

The joint area Z comprises an extension-frame-side joint area 81 as afront-side joint area for the extension frame 130 and asuspension-sub-frame-side joint area 82 as a rear-side joint area forthe suspension sub frame 110. The extension-frame-side joint area 81 isshorter than the suspension-sub-frame-side joint area 82 in the vehiclelongitudinal direction.

Since it is avoided that the extension-frame-side joint area 81 isimproperly long as described above, it is suppressed that appropriatedeformation of the extension frame 130 is blocked by the second crossmember 150 when the impact load is inputted from the vehicle forwardside. Accordingly, the impact absorption function of the extension frame130 can be properly performed.

Meanwhile, since the suspension-sub-frame-side joint area 82 is set tobe relatively long, the rigidity and strength of the suspension subframe 110 against the load in the vehicle longitudinal direction isproperly improved. Accordingly, the suspension sub frame 110 canproperly perform the function as the load receiving portion, so that theextension frame 130 can properly perform the impact absorption function.

As shown in the bottom view of FIG. 6, the above-described front-sidebracket 63 to support the lower arm 60 is attached to the connectionportion 80 of the extension frame 130 and the suspension sub frame 110from the vehicle outward side. The front-side bracket 63 is joined to arange over the lower face portion 132 a of the extension frame 130 andthe lower face portion 115 a of the suspension sub frame 110 at an areaW which is continuous in the vehicle longitudinal direction.

Thereby, the connection portion 80 of the extension frame 130 and thesuspension sub frame 110 is reinforced by the side portion 152 of thesecond cross member 150 particularly at its inward side, and reinforcedby the front-side bracket 63 at its outward side. Consequently, bendingdeformation of the connection portion 80 of the both frames 110, 130 canbe suppressed more effectively.

Further, since the front-side bracket 63 is used for reinforcing theoutward side of the connection portion 80, the reinforcement is attainedwithout adding any special reinforcing member.

As described, since the suspension sub frame structure of the presentinvention can compatibly attain effectively performing the respectivefunctions of the extension frame and the suspension sub frame andsuppressing the bending or breakage of the connection portion of theseframes, suppressing the increase of the vehicle weight, the presentsuspension sub frame structure is properly usable in a vehicle-bodymanufacturing industrial field of the vehicle.

What is claimed is:
 1. A suspension sub frame structure, comprising: asuspension sub frame provided to extend in a vehicle longitudinaldirection and supporting a suspension member of a front wheel; anextension frame provided to extend forwardly from a front end of thesuspension sub frame and having lower rigidity against a load applied inthe vehicle longitudinal direction than the suspension sub frame; and across member provided to extend in a vehicle width direction on aninward side, in the vehicle width direction, of the suspension sub frameand the extension frame, wherein said cross member is joined to saidsuspension sub frame and said extension frame at a joint area which iscontinuous in the vehicle longitudinal direction; and wherein said jointarea comprises a front-side joint area where said cross member is joinedto said extension frame and a rear-side joint area where said crossmember is joined to said suspension sub frame, and said front-side jointarea is shorter than said rear-side joint area.
 2. The suspension subframe structure of claim 1, wherein said cross member comprises anupper-face joint portion which is joined to an upper face of saidextension frame and an upper face of said suspension sub frame at saidjoint area and a lower-face joint portion which is joined to a lowerface of said extension frame and a lower face of said suspension subframe at said joint area.
 3. The suspension sub frame structure of claim2, wherein a bracket to make said suspension sub frame support saidsuspension member is attached to said extension frame and saidsuspension sub frame at an area which is continuous in the vehiclelongitudinal direction.
 4. The suspension sub frame structure of claim1, wherein a bracket to make said suspension sub frame support saidsuspension member is attached to said extension frame and saidsuspension sub frame at an area which is continuous in the vehiclelongitudinal direction.